This invention relates to a surface heat treating apparatus utilizing laser beam.
When the surface of a workpiece is heat-treated in use of a laser beam transmitted from a laser oscillator, operational characteristics depend much on the configuration of the focused laser beam.
FIG. 1 illustrates a conventional surface heat-treating apparatus utilizing laser beam. In this apparatus, a laser beam 1 emitted from a laser beam oscillator, not shown, is converged by means of a plane mirror 2 and a concave cylindrical mirror 3 on a surface of a workpiece W for executing heat-treatment on the surface. In this case, the focused heat-treating area on the surface is made into an elongated elliptical configuration, so that heat energy of the laser beam imparted to the surface of the workpiece becomes high at the central portion 4a of the elliptical heat-treating area 4 and low at both ends 4b and 4c thereof. More specifically, when a surface heat-treatment is performed, it is required that the focused heat-treating area is provided with predetermined amounts of length and width, and hence the focus of the optical system in the conventional apparatus has to be adjusted, i.e. shifted, so that the heat-treating area 4 has substantially the elliptical configuration, wherein the heat energy of laser beam is made high in the central portion and low in the end portions of the ellipse. Such a distribution of heat energy, however, has entailed uneven depth Ho in the surface heat-treatment of the workpiece W.